Method of manufacturing lithographic printing plate

ABSTRACT

A method for manufacturing a lithographic printing plate is provided in which conditions for heating a support and a photosensitive coated layer in a drying and heating step can be changed rapidly over a wide range, and the photosensitive coated layer and the support are heated without being contacted.

This is a continuation of application Ser. No. 10/984,908 filed Nov. 10,2004, which is a Continuation Application of U.S. application Ser. No.09/895,264 filed Jul. 2, 2001, now U.S. Pat. No. 6,933,017. The entiredisclosures of the prior application Ser. Nos. 10/984,908 and 09/895,264are considered part of the disclosure of the accompanying continuationapplication and are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing alithographic printing plate, and in particular, to a method ofmanufacturing a lithographic printing plate which is suited to themanufacturing of digital direct printing plates which are applied todirect plate-making systems.

2. Description of the Related Art

A so-called conventional printing plate is widely used as a conventionalphotosensitive lithographic printing plate. After this conventionalprinting plate is mask-exposed (planarly exposed) via a lith film, thenon-image portions of the photosensitive layer are dissolved andremoved, such that the printing plate carries a desired image.

In recent years, digitizing techniques for electronically processingimage information by using computers have come into wider use, and newplate-making techniques corresponding to these digitizing techniqueshave come to be put into practice. Specifically, light having highdirectivity, such as laser light, is modulated in accordance withdigitized image information. By scan-exposing an original plate of alithographic printing plate by using this laser light, acomputer-to-plate (CTP) technique can be realized in which a printingplate is manufactured directly without use of a lith film. The demandfor so-called digital direct plates which are suitable for this CTPtechnique continues to increase.

It is known that the quality of such a digital direct printing plate(i.e., the stability of the sensitivity, the scratch resistance, theability to withstand repeated printing, and the like) is more easilyaffected, than the quality of a conventional printing plate is, by thedrying conditions or the heating hardening conditions (curingconditions) of the photosensitive coated layer formed on the support. Inparticular, it is known that quality is affected by the heatingconditions (temperature and time) during curing in which the support andthe photosensitive coated layer are heated in order to accelerate thehardening of the photosensitive coated layer after evaporating anddrying have been carried out until the organic solvent of thephotosensitive coated layer is contained in a predetermined amount.Specifically, for example, when a plurality of types of digital directprinting plates, which differ only in that the thicknesses of theirrespective supports (which are formed by aluminum plates or the like)differ, are manufactured, if these supports and photosensitive coatedlayers are heated under the same conditions, differences in quality ofthe supports of the digital direct printing plates, which differences inquality are of an extent that cause problems in practice, arise due tothe differences in the heat capacities of the supports.

Further, in conventional lithographic printing plate manufacturingprocesses, the drying process and the curing process for the support andthe photosensitive coated layer are not clearly separated. For example,as disclosed in Japanese Patent Application Publication (JP-B) No.6-24673, while a support on which a photosensitive coated layer isformed is conveyed in one direction, drying and curing are carried outby a hot-air drying system drying device which blows out hot air into aheating furnace disposed along the conveying path of the support.However, in this hot-air drying system drying device, it is difficult tochange the heating conditions within a short period of time.Accordingly, when the thickness or the width or the like of the supportis changed, in order to change the heating conditions for the supportand the photosensitive coated layer, in most cases, the conveying speedof the support, i.e., the speed of manufacturing the lithographicprinting plate, must be changed, and it is difficult to stabilize theproduction speed of digital direct printing plates.

Further, it has recently become clear that, in order to make the quality(i.e., the stability of the sensitivity, the scratch resistance, theability to withstand repeated printing, and the like) of digital directprinting plates sufficiently high and stable, there is the need tosupply a great amount of heat to the photosensitive coated layer at thetime of curing, as compared with conventional printing plates. (Withregard to this point, refer to, for example, Japanese Patent ApplicationNo. 11-301240, the applicant of which is the same as the applicant ofthe present application.) Thus, when digital direct printing plates andconventional printing plates are to be manufactured by using the sameequipment, the manufacturing speeds are controlled by the heatingcapacities with respect to the supports and the photosensitive coatedlayers, and the speed of manufacturing the digital direct printing platemust be decreased greatly as compared to that of the conventionalprinting plate.

As a means for overcoming the above-described insufficient heatingcapacity, JP-B No. 6-49175 discloses a method of supplying a largeamount of heat to a support in a short time by heating rollers whichcontact the reverse surface of the support. Further, Japanese PatentApplication Laid-Open (JP-A) No. 2-227160 discloses a method ofcontrolling an amount of heat supplied to a support by changing the timeover which heating rollers contact a support. However, when a support isheated by these methods, minute scratches are formed in the reversesurface of the support by the heating rollers due to the supportexpanding or contracting due to the temperature difference between thesupport and the heating rollers, or due to the linear speed of theheating rollers and the conveying speed of the support not being equalor the like. These minute scratches do not present problems in practicein conventional printing plates. However, with digital direct printingplates, there are cases in which the photosensitive coated layer isscratched and problems arise with respect to quality, at the time thatthe support is wound up in a coil form or at the time that pluralprinting plates are stacked.

Thus, there is the demand for a technique for manufacturing high qualitydigital direct printing plates stably and at a low cost, in which theconditions for the heating of the support and the photosensitive coatedlayer during a drying and heating process can be changed quickly withina wide range, and heating can be carried out without the support and thephotosensitive coated layer being contacted, without greatly remodelingthe equipment for manufacturing conventional printing plates.

SUMMARY OF THE INVENTION

In view of the aforementioned, an object of the present invention is toprovide a method for manufacturing a lithographic printing plate inwhich the conditions for the heating of a support and a photosensitivecoated layer during a drying and heating process can be changed quicklywithin a wide range, and heating can be carried out without thephotosensitive coated layer and the support being contacted.

A first aspect of the method for manufacturing a lithographic printingplate of the present invention comprises: a drying and heating stepwherein, while a strip-shaped support, on which a photosensitive coatingsolution containing an organic solvent is coated such that aphotosensitive coated layer is formed by the photosensitive coatingsolution, is continuously conveyed, the photosensitive coated layer isdried by a first heating means to a dry-to-touch state, and the supportand the photosensitive coated layer are heated by a second heating meansprovided at a downstream side of the first heating means so thathardening of the photosensitive coated layer is promoted.

In accordance with the above-described method for manufacturing alithographic printing plate, in the drying and heating step, while thestrip-shaped support on which the photosensitive coated layer is formedis continuously conveyed, the photosensitive coated layer is dried bythe first heating means to a dry-to-touch state, and the support and thephotosensitive coated layer are heated by the second heating means sothat hardening of the photosensitive coated layer is promoted. Thesupport and the photosensitive coated layer are made to be sufficientlyhigh temperatures by the first heating means, and the drying of thephotosensitive coated layer sufficiently progresses, and the support andthe photosensitive coated layer can be supplied to the second heatingmeans. Thus, it suffices for the second heating means to supply, to thesupport and the photosensitive coated layer, only an amount of heatwhich is substantially equivalent to an amount of heat required foradjusting the temperature.

As a result, a heating device, which is a heat radiation system deviceor an induction heating system device or the like in which adjustment ofthe amount of supplied heat can be carried out in a short time, can beused as the second heating means. Thus, the conditions of heating thesupport and the photosensitive coated layer can be changed rapidly andover a wide range, and further, the support and the photosensitivecoated layer can be heated without being contacted.

Here, the dry-to-touch state of the photosensitive coated layer means astate in which, even if the surface of the photosensitive coated layeris touched by a finger, the photosensitive coated layer does not adhereto the finger. The liquid viscosity of the photosensitive coated layerat this time is generally 10⁸ to 10¹⁰ poise or more. As a specificexample of the heating conditions by the first heating means, while thephotosensitive coated layer is heated by the first heating means to 90°C. or more and preferably 100° C. or more, the amount of organicsolution remaining in the photosensitive coated layer is 5 wt % or less,and preferably 3 wt % or less, of the photosensitive coated layer whichis substantially completely dried.

Although the heating system of the first heating means is notparticularly limited, a hot air drying method is preferable from thestandpoints of the explosion-proof property and equipment costs, becausethe photosensitive coated layer contains an organic solvent. In order toprevent non-uniform blowing, it is preferable that, in the initialstages of drying, slow drying is carried out in which the temperatureand the air speed are suppressed, and towards the latter half, thetemperature and the amount of air are gradually increased.

At the point in time that the photosensitive coated layer is supplied tothe first heating means, the photosensitive coated layer contains alarge amount of organic solvent. Thus, the device forming the firstheating means necessitates an explosion-proof structure. However, at thepoint in time when the photosensitive coated layer is supplied to thesecond heating means, the amount of the organic solvent remaining in thephotosensitive coated layer is 5 wt % or less. Thus, the device formingthe second heating means does not require an explosion-proof structure.Accordingly, separating the first heating means and the second heatingmeans structurally may be advantageous with regard to cost as well sincethe structure of the second heating means is not limited.

At the second heating means, the support and the photosensitive coatedlayer are heated with the main purpose being the heating and hardening(i.e., curing) of the photosensitive coated layer on the support. Atthis time, from the standpoint of the quality of the lithographicprinting plate, it is important to carry out heating accurately to atarget temperature which is suitable for the characteristics of thephotosensitive coated layer, and to maintain this target temperatureover a predetermined period of time. In the same way as the firstheating means, the heating system of the second heating means is notparticularly limited. However, from the standpoint of preventingscratches in the reverse surface of the support, a non-contact system,such as a hot air system, a heat radiation system, an induction heatingsystem, or the like is more preferable than a contact heat transfersystem such as heating rollers. From the standpoint of being able tochange the heating condition in a short period of time, the heatradiation system and the induction heating system are more preferablethan the hot air system. Further, using a hot air system in combinationwith a heat radiation system or an induction heating system is alsoeffective in improving the heating efficiency.

A cooling zone, in which cooling is carried out by leaving the supportand the photosensitive coated layer to cool, may be provided between thefirst heating means and the second heating means. However, from thestandpoint of effectively using thermal energy, it is preferable thatthe time between the first heating means and the second heating means bemade as short as possible, and that the cooling of the photosensitivecoated layer and the support be suppressed.

Further, there is no need for the first heating means and the secondheating means to each be a single heating device. Each of the firstheating means and the second heating means can be structured by aplurality of drying devices disposed along the conveying path of thesupport.

The support is a plate-shaped object which is dimensionally stable, andexamples thereof include paper, paper on which a plastic (such aspolyethylene, polypropylene, polystyrene, or the like) is laminated, ametal plate (e.g., aluminum, zinc, copper, or the like), plastic film(e.g., cellulose diacetate, cellulose triacetate, cellulose propionate,cellulose acetate, cellulose acetate butyrate, cellulose nitrate,polyethylene terephthalate, polyethylene, polystyrene, polypropylene,polycarbonate, polyvinyl acetal, and the like), a paper or plastic filmon which a metal such as those mentioned above is laminated ordeposited, or the like. The support of the present invention ispreferably a polyester film or an aluminum plate, and thereamong, analuminum plate, which has good dimensional stability and is relativelyinexpensive, is particularly preferable. A preferable aluminum plate isa pure aluminum plate or an alloy plate whose main component is aluminumand which contains a trace quantity of a different element. A plasticfilm on which aluminum is laminated or deposited may be used. Examplesof the different element contained in the aluminum alloy are silicon,iron, manganese, copper, magnesium, chromium, zinc, bismuth, nickel,titanium, and the like. The amount of the different element contained inthe alloy is at most 10 wt %. In the present invention, the particularlypreferable aluminum is pure aluminum. However, manufacture of completelypure aluminum in refining technologies is difficult. Thus, a slightamount of a different element may be contained. The thickness of thealuminum plate used in the present invention is about 0.1 mm to 0.6 mm,and preferably 0.15 mm to 0.4 mm, and particularly preferably 0.2 mm to0.3 mm.

In a method for manufacturing a lithographic printing plate of a secondaspect of the present invention, in the method for manufacturing alithographic printing plate of the first aspect, a condition of heatingby the second heating means is controlled in accordance with a type ofthe photosensitive coated layer formed on the support, such that atemperature of the photosensitive coated layer immediately after heatingby the second heating means is a predetermined temperature which is setin accordance with the type of the photosensitive coated layer.

In accordance with the method for manufacturing a lithographic printingplate of the second aspect, a condition of heating by the second heatingmeans is controlled in accordance with the type of the photosensitivecoated layer formed on the support, such that the temperature of thephotosensitive coated layer immediately after heating by the secondheating means (i.e., the final temperature reached) is a predeterminedtemperature which is set in accordance with the type of thephotosensitive coated layer. In this way, in the drying and heatingstep, the final temperature reached by the photosensitive coated layerof the digital direct printing plate can accurately be made to be thetarget temperature. Thus, differences in quality of lithographicprinting plates, which result from differences in the final temperaturesreached, can be made to be sufficiently small, and qualities (stabilityof sensitivity, scratch resistance, ability to withstand repeatedprinting, and the like) of digital direct printing plates can bestabilized.

Namely, the extent to which the temperature of the photosensitive coatedlayer immediately after heating by the second heating means (the finaltemperature reached) affects the quality of the lithographic printingplate greatly depends on the type of the photosensitive coated layer.For example, with a conventional printing plate, if the remaining amountof organic solvent can be kept to 5 wt % or less, the effects on qualitydue to differences in the final temperatures reached by photosensitivecoated layers are small, and are not problematic. However, with regardto the thermal type digital direct printing plates disclosed in JP-ANos. 7-285275 and 11-44956 and the photopolymer type digital directprinting plates disclosed in Japanese Patent Application Nos. 11-623298and 11-301240, differences in the final temperatures reached by thephotosensitive (heat-sensitive) coated layers result in greatdifferences in quality, and it is necessary to precisely keep the finaltemperature reached within a target range.

Specifically, for a thermal type digital direct printing plate, thefinal reached temperature of the photosensitive coated layer must be 125to 145° C., and preferably 130 to 140° C. For photopolymer type digitaldirect printing plates, the final temperature reached by thephotosensitive coated layer must be 100 to 135° C., and preferably 105to 130° C.

For processless printing plates and lithographic printing plates using asilver salt diffusion transfer method which are currently beingresearched and developed (see, for example, JP-A No. 5-289348), thefinal temperature reached by the photosensitive coated layer must becontrolled to a narrow temperature range in the same way as, or evenmore so than, thermal type digital direct printing plates andphotopolymer type digital direct printing plates. With these digitaldirect printing plates which are currently being researched anddeveloped, the precision required of the final temperature reached bythe photosensitive coated layer is within 10° C., and more preferablywithin 5° C. The present invention greatly contributes to an earlyrealization of products of such printing plates which are currentlybeing researched and developed.

In a method for manufacturing a lithographic printing plate of a thirdaspect of the present invention, in the method for manufacturing alithographic printing plate of the first aspect or the second aspect, ina case in which thicknesses and widths of supports supplied to thesecond heating means continuously change, a condition of heating thesupports and photosensitive coated layers by the second heating meanschanges in accordance with the thicknesses and the widths of thesupports.

In accordance with the method for manufacturing a lithographic printingplate of the third aspect, in a case in which the thickness and thewidth of the support supplied to the second heating means change, acondition of heating the support and the photosensitive coated layer bythe second heating means is changed in accordance with the thickness andthe width of the support. In this way, because the condition of heatingby the second heating means can be changed quickly in accordance withchanges in the dimensions of the supports, even if the dimensions of thesupports which are being conveyed continuously vary, the finaltemperatures reached by the photosensitive coated layers can beaccurately be made to be the target temperatures without varying theconveying speed of the supports.

Namely, in a case in which, in the drying and heating process, thesupport and the photosensitive coated layer are heated under a constantheating condition, when a one support, which has a different dimension(thickness or width) than another support conveyed continuously at theupstream side, is connected to the final end portion of the othersupport, the heat capacity per unit length of the support changes fromthe portion at which the supports are connected. Thus, a change in thefinal temperature reached by the photosensitive coated layer arises inaccordance with this change in the dimensions of the support.Accordingly, in a case in which the dimensions of the supports changeduring the manufacturing of digital direct printing plates, the heatingconditions for the photosensitive coated layer and the support must bechanged rapidly in accordance with the change in the dimensions of thesupport.

However, in a method in which the photosensitive coated layer is driedby the photosensitive coated layer and the support being heated by asingle hot air type drying device which is provided as the first heatingmeans, it is difficult to change in a short period of time the amount ofheat supplied, per unit time, to the photosensitive coated layer and thesupport. In most cases, when the dimensions of the support change, themanufacturing speed or the heating conditions of the lithographicprinting plates are changed, and the amount of supplied heat is changedin accordance with the dimensions of the support or the type ofphotosensitive coated layer. As a result, as compared with conventionalprinting plates, produceability in manufacturing digital direct printingplates is unstable, and a problem arises in that the costs involved inmanufacturing digital direct printing plates increase.

Here, for example, the above-described heat radiation system orelectromagnetic induction heating system drying device is used as thesecond heating means. The target temperature at the exit of the dryingand heating process is set in accordance with the type (product type) ofthe photosensitive coated layer. Thus, it is effective to use the secondheating means together with hot air heating of a temperature which isslightly higher than the target temperature. In accordance with such adrying device, it is quite possible to change the heating conditionwithin one minute at the latest. Further, if a plurality of such dryingdevices are provided as the second heating means along the conveyingpath of the support and the amounts of heat supplied by each of theplurality of drying devices are controlled in accordance with changes inthe dimensions of the supports, the heating condition can be changed inan even shorter period of time.

In a method of manufacturing a lithographic printing plate of a fourthaspect of the present invention, in the method of manufacturing alithographic printing plate of any of the first second or third aspects,after hot air drying of the coated layer by the first heating means, thesecond heating means radiates mid-infrared radiation or far infraredradiation to the photosensitive coated layer and the support so as toheat the support and the photosensitive coated layer.

In accordance with the method of manufacturing a lithographic printingplate of the fourth aspect, after hot air drying of the coated layer bythe first heating means, the second heating means radiates mid-infraredradiation or far infrared radiation to the photosensitive coated layerand the support so as to heat the support and the photosensitive coatedlayer. In this way, the photosensitive coated layer can be efficientlyheated and dried without there being fogging of the photosensitivecoated layer.

It has been conventionally thought that, in a lithographic printingplate production line, drying and curing of a photosensitive coatedlayer by an infrared radiation system drying device was difficult due toconcerns relating to ignition of and generation of fogging in thephotosensitive coated layer which contains an organic solvent. Namely,when an infrared radiation system drying device was used, there was thefear that the organic solvent would ignite if the surface temperaturewas set high, and that, if the surface temperature was lowered to theignition point or lower, the drying efficiency would be markedlyinferior to that of a hot air system. Further, electrical circuits, forwhich there is the concern of generation of sparks, were set under hightemperatures near the photosensitive coated layer. For these reasons,measures for preventing explosions in infrared radiation system dryingdevices were difficult as compared to hot air system drying devices.

Further, some photosensitive coated layers are reactive with respect toinfrared radiation, and there is the fear that fogging may occur inphotosensitive coated layers due to infrared radiation. For this reasonas well, it was thought that infrared radiation system drying deviceswere unsuitable for application to the processes of drying and heatinglithographic printing plates. In particular, in thermal type digitaldirect printing plates, the exposure source is an infrared radiationlaser (830 nm), and the photosensitive coated layer is heat-sensitive.Thus, there were many concerns relating to quality when using, as theheat source, an infrared radiation radiating device with a surfacetemperature (of 300° C. or more) which had a better heating efficiencythan a hot air system.

While taking the above circumstances into consideration, the presentinventors studied using an infrared radiation system drying device as asecond heating means. As a result, the present inventors confirmed thata photosensitive coated layer has absorbing regions at a mid-infraredregion (2 to 4 μm) and a far infrared region (4 to 1000 μm), and thatthe heat generating efficiency thereof is good. Further, the presentinventors confirmed that infrared radiation (a surface temperature of800° C. or less), which does not contain wavelengths in the nearinfrared region of 1 μm or less, does not effect the quality of thephotosensitive coated layer nor the thermal type digital direct printingplate. Further, because the photosensitive coated layer is dried by thefirst heating means to a dry-to-touch state, at the time of heating bythe second heating means, there is no fear that the photosensitivecoated layer and the vaporized components from the photosensitive coatedlayer will ignite, and there is no need to take measures to make thedevice forming the second heating means explosion-proof.

By using an infrared radiation system drying device as the secondheating means, as compared to a hot air system drying device, theheating condition can be changed quickly, less space is required for thedevice, and the equipment costs can be kept down. The method forchanging the heating conditions at this time may be the changing of thesurface temperature of an infrared radiation radiating device, thechanging of the radiating surface area of an infrared radiationradiating device, the changing of the distance between the support andan infrared radiation radiating device, or the like, but is not limitedto these methods.

In a method of manufacturing a lithographic printing plate of a fifthaspect of the present invention, the method of manufacturing alithographic printing plate of any of the first second, third or fourthaspects further comprises a cooling step in which the support and thephotosensitive coated layer are forcibly cooled by a cooling meansprovided at a downstream side of the second heating means.

In accordance with the method of manufacturing a lithographic printingplate of the fifth aspect, the support and the photosensitive coatedlayer are forcibly cooled by a cooling means provided at a downstreamside of the second heating means. In this way, as compared with a casein which the photosensitive coated layer is left to cool naturally, thesurface temperature of the photosensitive coated layer can be decreasedin a short time. Thus, there are fewer restrictions on the layout ofconveying members such as conveying rollers and the like, and the timeuntil an overcoat layer can be coated on the photosensitive coated layercan be shortened.

Namely, immediately after heating by the second heating means, thesurface temperature of the photosensitive coated layer is generally 100°C. or more. When a member such as a conveying roller or the likecontacts the surface of the photosensitive coated layer which is in sucha high temperature state, there is the concern that the photosensitivecoated layer may be peeled off. Further, in a photopolymer type digitaldirect printing plate, an overcoat layer is coated and formed as a layeron the photosensitive coated layer in order to cut-off oxygen. However,when the surface temperature of the photosensitive coated layer is high,there is the concern that there may be non-uniform coating of theovercoat layer.

Such problems can be overcome by lowering the temperature of thephotosensitive coated layer by a cooling step to 50° C. or less, andpreferably to 40° C. or less. Here, the method for forcibly cooling thephotosensitive coated layer and the support may be any of various typesof cooling methods other than naturally cooling the photosensitivecoated layer and the support which are being conveyed, for example, anair-cooling system in which low temperature air is blown out onto thephotosensitive coated layer, or a cooling roller system in which a lowtemperature cooling roller is made to contact the reverse surface of thesupport or the like. However, with a contact-type cooling method such asa cooling roller system or the like, in the same way as with a heatingroller system, there is the fear that scratches may be formed in thesupport, and thus, a non-contact type cooling method such as anair-cooling system or the like is preferable.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a structural view which schematically illustrates alithographic printing plate production line relating to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a method of manufacturing a lithographic printing platerelating to an embodiment of the present invention will be describedwith reference to the drawing.

FIG. 1 illustrates a lithographic printing plate production linerelating to an embodiment of the present invention. A device (not shown)for feeding out aluminum plates 12 serving as supports is provided atfurthest upstream side of a production line 10. This feed-out devicefeeds-out the aluminum plates 12, which are of a thickness of from 0.1to 0.6 mm, to the downstream side at a conveying speed corresponding tothe speed of manufacturing the lithographic printing plates at theproduction line 10. A plurality of conveying rollers 14 are providedalong the conveying path of the aluminum plates 12 at the productionline 10. While the aluminum plate 12 is guided by the plural conveyingrollers 14, the aluminum plate 12 receives conveying force from aconveying motor (not shown) via the conveying rollers 14, and isconveyed downstream at a predetermined speed.

At the production line 10, first, the configuration of the aluminumplate 12, which is fed-out toward the downstream side from the feed-outdevice, is corrected and the requisite planarity of the aluminum plate12 is obtained by a correcting device (not shown) such as a rollerleveler, a tension leveler or the like for improving planarity. Next,before surface roughening of the aluminum plate 12, if desired, adegreasing processing is carried out by, for example, a surfactant, anorganic solvent, or an alkaline aqueous solution for removing therolling oil from the surface of the aluminum plate 12. The roughening ofthe surface of the aluminum plate can be carried out by any of variousmethods, and is carried out, for example, by method of mechanicallyroughening the surface, a method of dissolving and roughening thesurface electrochemically, or a method of selectively dissolving thesurface chemically.

Any of known methods such as a ball polishing method, a brush polishingmethod, a blast polishing method, a buff polishing method, or the like,can be used as the mechanical method. Further, an example of the methodof roughening the surface electrochemically is a method carried out byalternating current or direct current in a hydrochloric acid or nitricacid electrolytic solution. Moreover, a combination of both types ofmethods can be used as disclosed in JP-A No. 54-63902. The aluminumplate 12, whose surface has been roughened in this way, is subjected ifnecessary to an alkali etching processing or a neutralizing processing,and thereafter, if desired, is subjected to an anodizing treatment inorder to improve the water retaining property of the surface and thewear resistance. Any of various electrolytes which form a porous acidicfilm can be used as the electrolytes used in the anodizing treatment ofthe aluminum plate 12, and generally, sulfuric acid, phosphoric acid,oxalic acid, chromic acid, or a mixed acid thereof is used. Theconcentration of the electrolyte is selected appropriately in accordancewith the type of electrolyte.

Because the conditions of the anodizing treatment vary in accordancewith the electrolyte which is used, the conditions cannot be stipulateduniformly. However, generally, the following conditions are appropriate:an electrolyte concentration of a 1 to 80 wt % solution, a solutiontemperature of 5 to 70° C., a current density of 5 to 60 A/dm², avoltage of 1 to 100 V, and an electrolyzing time of 10 seconds to 5minutes. If the amount of the anodized film is less than 1.0 g/m², theability to withstand repeated printing deteriorates, it is easy for thenon-image portions of the lithographic printing plate to be scratched,and it is easy for so-called “scratch dirtying” to occur in which inkadheres to the scratched portions at the time of printing. After theanodizing treatment has been carried out, if needed, the aluminumsurface is subjected to a hydrophilizing treatment. Examples ofhydrophilizing treatments which can be used in the present invention arethe alkali metal silicate (e.g., sodium silicate aqueous solution)methods disclosed in U.S. Pat. Nos. 2,714,066, 3,181,461, 3,280,734, and3,902,734. In these methods, the support is processed by being immersedin a sodium silicate aqueous solution or electrolyzed. In addition, themethod of carrying out processing in potassium fluorozirconate disclosedin JP-B No. 36-22063, or the methods of carrying out processing inpolyvinylphosphonic acid disclosed in U.S. Pat. Nos. 3,276,868,4,153,461, and 4,689,272, or the like may be used.

Next, if needed, an undercoat layer is formed on the aluminum plate 12before formation of the photosensitive coated layer. Any of variousorganic compounds can be used as the component of the undercoat layer,and can be selected from phosphonic acids having an amino group such ascarboxymethyl cellulose, dextrin, gum arabic, 2-aminoethyl phosphonate,and the like; organic phosphonic acids which may have a substituent suchas phenyl phosphonate, naphthyl phosphonate, alkyl phosphonate,glycerophosphonic acid, methylene diphosphonate, ethylene diphosphonate,and the like; organic phosphoric acids which may have a substituent suchas phenyl phosphate, naphthyl phosphate, alkyl phosphate,glycerophosphoric acid, and the like; organic phosphinic acids which mayhave a substituent such as phenyl phosphinate, naphthyl phosphinate,alkyl phosphinate, glycerophosphinic acid, and the like; amino acidssuch as glycine, β-alanine, and the like; hydrochlorides of amineshaving a hydroxy group such as hydrochloride of triethanol amine, andthe like; and the like. Or, a mixture of two or more of the abovecompounds may be used.

The organic undercoat layer may be formed by a method such as thefollowing: a method in which a solution is coated on an aluminum plateand dried, the solution being formed by dissolving one or more of theabove-listed organic compounds in water or an organic solvent such asmethanol, ethanol, or methylethyl ketone or the like, or a mixedsolution thereof; and a method in which an aluminum plate is immersed ina solution formed by dissolving one or more of the above-listed organiccompounds in water or an organic solvent such as methanol, ethanol, ormethylethyl ketone or the like, or a mixed solution thereof, such thatthe organic compound(s) is (are) adsorbed, and thereafter, washing thealuminum plate with water or the like and drying the aluminum plate suchthat an organic undercoat layer is formed. In the former method, asolution having a concentration of the organic compound(s) of 0.05 to 10wt % can be coated by any of various methods. In the latter method, theconcentration of the solution is 0.01 to 20 wt % and preferably 0.05 to5 wt %, and the immersion temperature is 20 to 90° C. and preferably 25to 50° C., and the immersion time is 0.1 seconds to 20 minutes andpreferably 2 seconds to 1 minute. The pH of the solution which is usedcan be adjusted by a basic substance such as ammonia, triethylamine,potassium hydroxide, or the like, or by an acidic substance such ashydrochloric acid, phosphoric acid, or the like. Further, a yellow dyefor improving the tone reproduction of the image recording material canbe added. The covering amount of the organic undercoat layer isappropriately 2 to 200 mg/m², and preferably 5 to 100 mg/m². If thecovering amount is less than 2 mg/m², the ability to withstand repeatedprintings is insufficient. The same holds if the coated amount isgreater than 200 mg/m².

As shown in FIG. 1, at the production line 10, a coating device 16 forcoating a photosensitive coating solution onto the aluminum plate 12 isprovided at the downstream side of the anodizing device. At the coatingdevice 16, while the reverse surface side of the aluminum plate 12 issupported by a support roller 18, a photosensitive coating solution isapplied to the surface of the aluminum plate 12 so as to form aphotosensitive coated layer. The photosensitive coated layer is anorganic solvent photosensitive coated layer which is photosensitive orheat-sensitive.

Namely, the photosensitive coated layer is a photosensitive coated layerin a conventional positive printing plate having a photosensitive coatedlayer whose main components are naphthoquinone diazide and phenol resin;a conventional negative printing plate having a photosensitive coatedlayer whose main components are a diazonium salt and an alkali resin ora urethane resin; a photopolymer digital direct printing plate having aphotosensitive coated layer formed from an ethylene unsaturatedcompound/a photopolymerizable initiator/a binder resin; a thermalpositive digital direct printing plate having a photosensitive coatedlayer whose main components are phenol resin/acrylic resin/an IR dye;and a thermal negative digital direct printing plate having aphotosensitive coated layer formed from a thermal acid generator/athermal crosslinking agent/a reactive polymer/and an IR dye. Further,the photosensitive coated layer may be an organic solvent typephotosensitive coated layer of a thermal abrasion type processlessprinting plate, a heat-fusible processless printing plate, or alithographic printing plate using a silver salt diffusion transfermethod.

Examples of the organic solvent are ethylene chloride, cyclohexanone,methylethyl ketone, methanol, ethanol, propanol, ethyleneglycolmonomethylether, 1-methoxy-2-propanol, 2-methoxyethyl acetate,1-methoxy-2-propyl acetate, dimethoxyethane, methyl lactate, ethyllactate, N,N-dimethylacetoamide, N,N-dimethylformamide, tetramethylurea, N-methylpyrrolidone, dimethylsulfoxide, sulfolane,γ-butyrolactone, toluene, and the like. However, the organic solvent isnot limited to these examples. A single one of these solvents or amixture of these solvents may be used. The concentration of theaforementioned components (the total solids including additives) in thesolvent is preferably 1 to 50 wt %. Further, the coated amount (solids)on the support obtained after coating and drying varies in accordancewith the application, but generally, for a photosensitive printingplate, a coated amount of 0.5 to 5.0 g/m² is preferable.

Any of various known methods can be used as the method for applying thephotosensitive coating solution onto the aluminum plate 12, and examplesinclude bar coater coating, rotary coating, spray coating, curtaincoating, dip coating, air knife coating, blade coating, roll coating,and the like. The smaller the coated amount, the greater the apparentsensitivity, but the worse the film characteristics of thephotosensitive film. A surfactant for improving the coatability, e.g.,the fluorine based surfactants disclosed in JP-A No. 62-170950, can beadded to the photosensitive layer of the present invention. Thepreferable added amount is 0.01 to 1 wt % and more preferably 0.05 to0.5 wt % of the total printing plate material.

As shown in FIG. 1, at the production line 10, a hot air drying device20 serving as a first heating means is disposed downstream of thecoating device 16. The hot air drying device 20 has a drying furnace 22having an explosion-proof and thermally insulated structure and formedin a box-shape which is elongated along the conveying direction of thealuminum plate 12. A plurality of support rollers 24 are disposed in thedrying furnace 22 along the conveying path of the aluminum plate 12.

Openings 26, 28 are formed in the upstream side end surface and thedownstream side end surface, respectively, along the conveying directionof the aluminum plate 12 in the drying furnace 22. These openings 26, 28are the entrance and exit of the aluminum plate 12 into and from thedrying furnace 22. The aluminum plate 12 which is supplied into thedrying furnace 22 from the opening 26 is conveyed in the drying furnace22 while the reverse surface side thereof is supported by the supportrollers 24, and is withdrawn to the exterior of the drying furnace 22from the opening 28. A partitioning wall 34, which divides the dryingfurnace 22 into an upstream side heating chamber 30 and a downstreamside heating chamber 32, is provided in the heating furnace 22. Movementof air between the heating chambers 30, 32 is suppressed by thepartitioning wall 34.

An air inlet 36 and an air outlet 38 are provided at the upstream sideheating chamber 30. A hot air generating device (not shown) is connectedto the air inlet 36 via a duct or the like. Further, an airflowregulating plate 40 is provided within the heating chamber 30 so as toface the air inlet 36. A plurality of slit-shaped blow-out holes areformed in the airflow regulating plate 40. The airflow regulating plate40 regulates the flow of the high temperature air (hot air) such thatthe high temperature air supplied into the heating chamber 30 from theair inlet 36 flows along the surface of the aluminum plate 12.

At this time, a high temperature gas of 50 to 100 m³/min per 1 m widthof the aluminum plate 12 is supplied to the air inlet 36, and thetemperature of this high temperature gas is controlled to 50 to 80° C.In this way, about 80% of the organic solvent contained in thephotosensitive coated layer at the time of coating onto the surface ofthe aluminum plate 12 is evaporated in the heating chamber 30, and thephotosensitive coated layer can be changed into a film which is in asoft film state.

The downstream side heating chamber 32 as well is provided with an airinlet 42 and an air outlet 44, and a hot air generating device (notshown) is connected to the air inlet 42 via a duct or the like. Anairflow regulating plate 46 is provided in the heating chamber 32between the air inlet 42 and the aluminum plate 12. A plurality ofslit-shaped blow-out openings are formed in the airflow regulating plate46 so as to face the surface of the aluminum plate 12. The airflowregulating plate 46 regulates the flow of high temperature air (hot air)such that the high temperature air supplied into the heating chamber 32from the air intake 42 is blown substantially perpendicularly onto thesurface of the aluminum plate 12.

At this time, a high temperature gas of 50 to 100 m³/min per 1 m widthof the aluminum plate 12 is supplied to the air inlet 42, and thetemperature of this high temperature gas is controlled to 100 to 120° C.In this way, about 95% or more of the organic solvent contained in thephotosensitive coated layer at the time of coating onto the surface ofthe aluminum plate 12 is evaporated in the heating chamber 32, and thephotosensitive coated layer, which was in a soft film state, can be madeto be dry-to-touch.

As shown in FIG. 1, at the production line 10, a far infrared radiationheating device 50 serving as a second heating means is disposeddownstream of the hot air drying device 20. A heating furnace 52, whichis formed in a box-shape which is elongated along the conveyingdirection of the aluminum plate 12, is provided at the far infraredradiation heating device 50. A far infrared radiation heater 54 isdisposed within the heating furnace 52 so as to oppose the surface ofthe aluminum plate 12. Openings 58, 60 are formed in the upstream anddownstream side end surfaces along the aluminum plate 12 conveyingdirection in the heating furnace 52. These openings 58, 60 are theentrance and exit of the aluminum plate 12 into and from the heatingfurnace 52.

At the point in time when the aluminum plate 12 is withdrawn from thehot air drying device 20, the remaining amount of the organic solvent inthe photosensitive coated layer on the aluminum plate 12 is 5 wt % orless of the photosensitive coated layer in the dried state. At the pointin time when the aluminum plate 12 is supplied into the heating furnace52, the remaining amount of the organic solvent in the photosensitivecoated layer is even lower. Thus, there is no fear of ignitingoccurring. As a result, it suffices to not make the heating furnace 52an explosion-proof structure, and to make the heating furnace 52 athermally-insulated structure in order to improve the efficiency ofheating the aluminum plate 12 and the photosensitive coated layer.

At the production line 10, temperature sensors 62, 64 are disposedslightly upstream and slightly downstream, respectively, of the heatingfurnace 52 of the far infrared radiation heating device 50. Thesetemperature sensors 62, 64 measure the temperature of the surface of thealuminum plate 12, and output detection signals corresponding to theresults of measurement to a computing processing device 66. Either of acontact-type or non-contact-type temperature sensor can be used as thetemperature sensors 62, 64. However, in a case in which a contact-typetemperature sensor such as a thermistor is used, in order to prevent thephotosensitive coated layer from being scratched, it is necessary tomeasure the temperature of the reverse surface of the aluminum plate 12,and to correct this measured value to estimate the temperature of thephotosensitive coated layer. In contrast, use of a non-contact-typetemperature sensor such as a radiation temperature sensor isadvantageous from the standpoints of accuracy of measurement andreliability because the temperature of the surface of the photosensitivecoated layer can be directly measured.

The computing processing device 66 controls the amount of heat radiatedby the far infrared radiation heater 54 via a heater driving device 68.Further, in addition to the detection signals from the temperaturesensors 62, 64, production information from a higher order computer (notshown) is inputted to the computing processing device 66. Thisproduction information includes the type of the photosensitive coatedlayer and information relating to the dimensions (the thickness and thewidth) of the aluminum plate 12. Further, as shown in FIG. 1, aconnection detector 70 is provided at the upstream side of thephotosensitive coating solution coating device 16. The connectiondetector 70 is for detecting a connection portion between the aluminumplate 12 which is being dried and heated and the aluminum plate 12 whichis connected to the trailing end portion of that aluminum plate 12. Atthe connected portion between a pair of aluminum plates 12, usually, anotch portion which is notched from a side end toward the center isformed, and a connecting tape is adhered. Thus, if the notch portion orthe connecting tape can be detected optically or mechanically, theconnection portion between a pair of aluminum plates 12 can be detected.The detection signal from the connection detector 70 is also outputtedto the computing processing device 66. The computing processing device66 tracks the connection portions by using the position of detection bythe connection detector 70 as a starting point.

Here, when the computing processing device 66 recognizes, on the basisof the production information, that the dimension of the aluminum plate12 has changed, immediately before a connection portion between aluminumplates 12 reaches the far infrared radiation heating device 50 orsimultaneously with a connection portion reaching the far infraredradiation heating device 50, the computing processing device 66 changesthe amount of heat radiated from the far infrared radiation heater 54 inaccordance with the difference in the dimensions between the aluminumplates 12. Specifically, the computing processing device 66 changes theamount of heat radiated from the far infrared radiation heater 54 inaccordance with the difference in the heat capacities per unit length ofthe upstream and downstream aluminum plates 12. The width of variationin the amount of radiated heat at this time is a relatively small widthcorresponding to the difference in dimensions of the aluminum plates 12.Further, the amount of heat radiated from the far infrared radiationheater 54 can be changed quickly in accordance with the drive signal ofthe heater driving device 68. Thus, controlling the amount of heatradiated from the far infrared radiation heater 54 to the target heatamount is usually completed within one minute. Thereafter, on the basisof the detection signals from the temperature sensors 62, 64, thecomputing processing device 66 feedback-controls the amount of heatradiated from the far infrared radiation heater 54 such that thetemperature of the surface of the photosensitive coated layer fallswithin a target temperature range set in accordance with the type of thephotosensitive coated layer.

A far infrared radiation heater, whose far infrared radiation emittingbody is a ceramic, is appropriate for use as the far infrared radiationheater 54 of the present embodiment. A gas type or electrical type farinfrared radiation heater which allows the ceramic to become asufficiently high temperature is suitable. The far infrared radiationheater 54 may be tube-shaped or panel-shaped. However, a panel shape isoptimal from the standpoint of being able to independently set differentconditions in the conveying direction and the widthwise direction of thealuminum plate 12 which serves as a support. The surface temperature ofthe ceramic of the far infrared radiation heater 54 at this time must beat least 300° C. (λ max: 5.1 μm) at which the drying efficiency by thehot air system is excellent, and must be at most 800° C. (λ max: 2.7 μm)at which no wavelengths of 1 μm or less are included.

In the above-described far infrared radiation heating device 50, dryingis carried out until the amount of solvent remaining in thephotosensitive coated layer on the aluminum plate 12 is 5% or less, andthe photosensitive coated layer is made to be a sufficiently hightemperature (100° C. or more). Thus, the photosensitive coated layer andthe aluminum plate 12 are heated by the far infrared radiation heater 54with the main object being the hardening of the photosensitive coatedlayer. The final temperature which the photosensitive coated layerreaches at this time is 130 to 140° C. at a thermal type digital directprinting plate, and is 105 to 130° C. at a photopolymer type digitaldirect printing plate.

At the production line 10, a forced cooling type cooling device 72 isdisposed downstream of the far infrared radiation heating device 50. Asshown in FIG. 1, the cooling device 72 is provided with a cooling tank74 which is shaped as a box which is elongated along the conveyingdirection of the aluminum plate 12. Openings 76, 78 are formed at theupstream and downstream side end surfaces along the conveying directionof the aluminum plate 12 in the cooling tank 74. These openings 76, 78are an entrance and an exit of the aluminum plate 12 into and from thecooling tank 74.

Two sets of an air inlet 80 and an air outlet 82 are provided at thecooling tank 74, so as to correspond to the surface and the reversesurface of the aluminum plate 12 respectively. A cold air generatingdevice (not shown) is connected to both of the two air inlets 80 viaducts or the like. An airflow regulating plate 84 is disposed in thecooling tank 74 between the surface of the aluminum plate 12 and the airinlets 80. A plurality of slit-shaped blow-out openings are formed inthe airflow regulating plate 84 so as to face the surface of thealuminum plate 12. The airflow regulating plate 84 makes the lowtemperature air supplied into the cooling tank 74 from the air inlet 80into a low temperature airflow (cold air) which is blown substantiallyperpendicularly onto the surface of the aluminum plate 12. Further, theairflow regulating plate 84 makes the low temperature air supplied intothe cooling tank 74 from the air inlet 80 facing the reverse surfaceside of the aluminum plate 12 an airflow which flows along the reversesurface of the aluminum plate 12. Accordingly, the aluminum plate 12 andthe photosensitive coated layer which are being conveyed in the coolingtank 74 are forcibly cooled by a flow of low temperature air. At thistime, the temperature and the amount of the low temperature air suppliedinto the cooling tank 74 are respectively set such that thephotosensitive coated layer, which is heated by the far infraredradiation heating device 50 to 140° C. which is the maximum heatedtemperature, can be cooled to 40° C. or less.

At the production line 10, downstream of the cooling device 72, ifneeded, an overcoat layer can be formed on the photosensitive coatedlayer by applying PVA (polyvinyl alcohol) or the like for the purpose ofcutting off oxygen or the like. At this time, because the temperature ofthe surface of the photosensitive coated layer on the aluminum plate 12is 40° C. or less, no irregularities in coating are generated in theovercoat layer, and the overcoat layer can be hardened quickly.

The production of the web, which is the material of the digital directprinting plate and which is formed as described above, is completed.This web is wound-up in roll form by a web take-up device (not shown),so as to form a web roll. This web roll is supplied to a digital directprinting plate processing line. The web roll is subjected to processingssuch as an interleaf sheet for protection being adhered thereto, the webroll being cut into product sizes, and the like, such that digitaldirect printing plates which are products are manufactured.

EXAMPLES Example of Application to Thermal Positive Type Digital DirectPrinting Plate

A support and a photosensitive coated layer, which were materials for athermal positive type digital direct printing plate, were manufacturedexperimentally in accordance with the following methods.

{circle around (1)} Synthesis of Specific Copolymer P₁

31.0 g (0.36 mol) of methacrylic acid, 39.1 g (0.36 mol) of ethylchloroformate, and 200 ml of acetonitrile were placed in a 500 mlthree-necked flask equipped with a stirrer, a cooling tube and adropping funnel. While the flask was cooled in an ice water bath, themixture was stirred. 36.4 g (0.36 mol) of triethylamine was added tothis mixture by drops through the dropping funnel over about one hour.After this dropwise addition was completed, the ice water bath wasremoved, and the mixture was stirred for 30 minutes at room temperature.

To this reaction solution was added 51.7 g (0.30 mol) of p-aminobenzenesulfonamide, and the mixture was stirred for one hour while being heatedto 70° C. in an oil bath. After the reaction was finished, the mixturewas added to one liter of water while the water was being stirred. Theobtained mixture was stirred for 30 minutes. This mixture was filteredand the precipitate removed. The precipitate was made into a slurry byadding 500 ml of water, and thereafter, the slurry was filtered. Theobtained solid was dried to obtain a white solid ofN-(p-aminosulfonylphenyl)methacrylamide (yield: 46.9 g).

Next, 4.61 g (0.0192 mol) of N-(p-aminosulfonylphenyl)methacrylamide,2.94 g (0.0258 mol) of ethyl methacrylate, 0.80 g (0.015 mol) ofacrylonitrile, and 20 g of N,N-dimethylacetoamide were placed in a 20 mlthree-necked flask equipped with a stirrer, a cooling tube and adropping funnel. The mixture was stirred while being heated to 65° C. ina hot water bath. To this mixture was added 0.15 g of “V-65”(manufactured by Wako Junyaku KK), and while the temperature wasmaintained at 65° C., the mixture was stirred for 2 hours under anitrogen flow. To this reaction mixture, a mixture of 4.61 g ofN-(p-aminosulfonylphenyl)methacrylamide, 2.94 g of ethyl methacrylate,0.80 g of acrylonitrile, and 0.15 g of N,N-dimethylacetoamide and “V-65”was added dropwise by the dropping funnel over 2 hours. After thedropwise addition was completed, the obtained mixture was stirred fortwo hours at 65° C. After the reaction was completed, 40 g of methanolwas added to the mixture, cooling was carried out, and the obtainedmixture was added to two liters of water while the water was beingstirred. After the mixture was stirred for 30 minutes, the precipitatewas removed by filtration, and 15 g of a white solid was obtained bydrying. The weight average molecular weight (polystyrene standard) ofthis specific copolymer P₁ as measured by gel permeation chromatographywas 53,000.

{circle around (2)} Preparation of Support

An aluminum plate (material: JIS1050) of a thickness of 0.15 to 0.4 mmwas washed and degreased with trichloroethylene. Thereafter, the surfacewas roughened by using a nylon brush and a 400 mesh pumice—watersuspension. The aluminum plate was then washed well with water. Theplate was immersed for 9 seconds in a 25% sodium hydroxide aqueoussolution of 45° C. so that etching was carried out, and was washed withwater. Thereafter, the plate was immersed for 20 seconds in 20% nitricacid, and washed with water. The amount of etching of the roughenedsurface at this time was about 3 g/m². Next, a direct current anodizedfilm of 3 g/m² was formed on the aluminum plate by a 7% sulfuric acidelectrolytic solution with a current density of 15 A/dm². Thereafter,the plate was washed with water and dried. Then, the following undercoatsolution was applied thereto, and the coated film was dried for 1 minuteat 90° C. The coated amount of the coated film after drying was 10mg/m².

Undercoat Solution β-Alanine 0.5 g Methanol 95 g Water 5 g

Further, the aluminum plate was processed for 10 seconds at 30° C. in asodium silicate 2.5 wt % aqueous solution. The following undercoatsolution was coated, and the coated film was dried for 15 seconds at 80°C. so as to obtain the support. At this time, the coated amount of thecoated film after drying was 15 mg/m².

Undercoat Solution Compound of Chemical Formula 1 0.3 g Methanol 100 gWater 1 g Chemical Formula 1

molecular weight 28,000{circle around (3)} Formation of Photosensitive Coated Layer

A photosensitive coating solution having the following composition wascoated, such that the coated amount after drying was 1.8 g/m², on thesupport obtained as described above, so as to form a photosensitivecoated layer.

Specific copolymer P₁ 0.75 g m,p-Cresol novalak (m,p ratio = 6/4; 0.25 gweight average molecular weight: 3500; content of unreacted cresol: 0.5wt %) p-Toluenesulfonic acid 0.003 g Tetrahydrophthalic anhydride 0.03 gCyanine dye of Chemical Formula 2 0.017 g Dye in which the counter ionof 0.015 g Victoria Pure Blue BOH was replaced with a1-naphthalenesulfonic acid anion MEGAFAC F177 (fluorine based surfactant0.05 g manufactured by Dainippon Ink & Chemicals, Inc.) γ-Butylactone 10g Methylethyl ketone 10 g 1-Methoxy-2-propanol 1 g Chemical Formula 2Cyanine dye A

Next, the support and the photosensitive coated layer, which werematerials for a thermal positive type digital direct printing plate andwhich were manufactured in accordance with the above methods, wereheated by the hot air drying device 20 or the far infrared radiationheating device 50 of the production line 10 illustrated in FIG. 1, so asto prepare a sample of the digital direct printing plate. At this time,the thickness of the support (the aluminum plate) or the heatingconditions were changed in steps, and the qualities (the ability towithstand repeated printing, the developability, and the overallquality) were evaluated for each of the samples having the differentsupport thicknesses or heating conditions. The results are shown inTable 1.

Note that the x, Δ, and ◯ symbols used for the evaluation of quality inTable 1 are defined as follows.

-   -   x . . . did not measure up to quality stipulated by quality        standards (unsatisfactory quality)    -   Δ . . . although no problems in terms of quality standards,        slight faults with respect to quality occurred    -   ◯ . . . no faults with respect to quality

TABLE 1 hot air drying device far infrared radiation heating deviceability to conveying set exit surface set exit surface withstand speedthickness of temperature heating temperature temperature heatingtemperature repeated develop- overall (m/min) support (mm) (° C.) time(sec) (° C.) (° C.) time (sec) (° C.) printings ability quality 10 0.15150 60 145 — — — ◯ X X 0.30 141 ◯ Δ Δ 0.40 130 ◯ ◯ ◯ 15 0.15 45 141 ◯ ΔΔ 0.30 133 ◯ ◯ ◯ 0.40 121 Δ ◯ Δ 20 0.15 30 132 ◯ ◯ ◯ 0.30 123 Δ ◯ Δ 0.40109 X ◯ X 25 0.15 24 122 Δ ◯ Δ 0.30 115 X ◯ X 0.40 103 X ◯ X 0.15 117400 5 137 ◯ ◯ ◯ 0.30 109 123 Δ ◯ Δ 0.40 96 108 X ◯ X 0.15 118 500 144 ◯Δ Δ 0.30 109 129 ◯ ◯ ◯ 0.40 95 114 Δ ◯ Δ 0.15 116 600 153 ◯ X X 0.30 110142 ◯ Δ Δ 0.40 96 126 ◯ ◯ ◯

As is clear from the evaluations relating to developability in Table 1,when the final temperature reached in either the hot air drying device20 or the far infrared radiation heating device 50 was 140° C. or more,the developability deteriorated. When this temperature exceeded 145° C.,the developing was poor. Further, when the final temperature reached ateither of the hot air drying device 20 or the far infrared radiationheating device 50 was 125° C. or less, the ability to withstand repeatedprintings deteriorated, and when this temperature was 120° C. or less,problems arose with respect to quality.

In a case in which the support (aluminum plate) and the photosensitivecoated layer were heated by using only the hot air drying device 20 andwith the heating condition being constant (set temperature=150° C.), asample of an equivalent quality could not be produced if the conveyingspeed was not adjusted in accordance with the thickness of the support.Conversely, in a case in which an attempt was made to address theproblems with respect to quality by making the conveying speed of thesupport constant and changing the heating condition by the hot airdrying device 20, it was necessary to make the conveying speeds of othersupports match the conveying speed of the support requiring the largestamount of heat (i.e., the conveying speed of the thickest support), andthus, the produceability deteriorated.

On the other hand, in a case in which both the hot air drying device 20and the far infrared radiation heating device 50 were used, as comparedwith a case in which only the hot air drying device 20 was used, theconveying speed of the support could be made to be 1.25 to 2.5 timesfaster, and production at a line speed which was equivalent to that forconventional printing plates was possible. Further, by setting theheating conditions of the far infrared radiation heating device 50 inaccordance with a support thickness of 0.15 to 0.40 mm, the conveyingspeed of the support could be maintained sufficiently fast (25 m/min),and stable production of thermal type digital direct printing plateswhich had no faults with respect to quality was possible.

(Example of Application to Photopolymer Type Digital Direct PrintingPlate)

A support and a photosensitive coated layer, which were materials for aphotopolymer type digital direct printing plate, were manufacturedexperimentally in accordance with the following methods.

{circle around (1)} Synthesis of Polyurethane Resin

In a 500 ml three-necked, round-bottomed flask equipped with a condenserand a stirrer, 12.1 g (0.09 mol) of 2,2-bis(hydroxymethyl)propionic acidand 20.0 g (0.01 mol) of a diol compound (hydroxyl value: 56.9 mgKOH/g)were dissolved in 100 ml of N,N-dimethylacetyacedo. To this mixture wasadded 20.0 g (0.08 mol) of 4,4′-diphenylmethane diisocyanate and 3.4 g(0.02 mol) of hexamethylenediisocyanate, and the resultant mixture washeated and stirred for 5 hours at 100° C. Thereafter, the mixture wasdiluted with 200 ml of N,N-dimethylformamide and 400 ml of methylalcohol. The reaction solution was added to four liters of water whilestirring was carried out, and a white polymer was precipitated. Thispolymer P₂ was filtered out, was washed with water, and thereafter, wasdried in a vacuum so as to obtain 45 g of the polymer P₂. The weightaverage molecular weight (polystyrene standard) as measured by gelpermeation chromatography (GPC) was 50,000. Further, the amount ofcontained carboxyl groups (acid value) as measured by titration was 1.40meq/g.

{circle around (2)} Preparation of Support

The surface of an aluminum plate of a thickness of 0.15 to 0.4 mm wasroughened by using a nylon brush and a 400 mesh pumice stone watersuspension. The aluminum plate was then washed well with water. Theplate was immersed for 60 seconds in a 10 wt % sodium hydroxide aqueoussolution of 70° C. so that etching was carried out, and was washed withwater. Thereafter, the plate was washed in 20% nitric acid so as to beneutralized, and then washed with water. The plate was subjected to anelectrolytic surface roughening treatment at an anode time currentamount of 160 coulomb/dm² in a 1 wt % nitric acid aqueous solution byusing a sinusoidal alternating waveform current under the conditionVa=12.7 V. The surface roughness was measured and found to be 0.6 μm(expressed as Ra). Then, the aluminum plate was immersed in a 30 wt %sulfuric acid aqueous solution and subjected to death mat processing for2 minutes at 55° C. Thereafter, the aluminum plate was subjected to ananodizing treatment for 2 minutes in a 20 wt % sulfuric acid aqueoussolution at a current density of 2 A/dm² such that the anodized filmthickness was 2.7 g/m².

{circle around (3)} Method of Forming Photosensitive Coated Layer

A photosensitive coating solution (photopolymerizable photosensitivesolution) having the following composition was coated, such that thecoated amount after drying was 1.5 g/m², on the support obtained asdescribed above, so as to form a photosensitive coated layer.

Pentaerithritol tetraacrylate 1.5 g Polyurethane resin binder (polymerP₂) 2.0 g Sensitizing dye Dye-1 of (Chemical Formula 3) 0.1 gPhotopolymerization initiator S-1 0.2 g of Chemical Formula 3 Fluorinebased nonionic surfactant 0.03 g Copper phthalocyanine pigment (organic0.1 g polymer dispersed) Methylethyl ketone 20.0 g Propyleneglycolmonomethyl ether 20.0 g Chemical Formula 3 Sensitizing dye Dye-1

Photopolymerization initiator S-1

Next, the support and the photosensitive coated layer, which werematerials for photopolymer type digital direct printing plate and whichwere manufactured in accordance with the above methods, were heated bythe hot air drying device 20 or the far infrared radiation heatingdevice 50 of the production line 10 illustrated in FIG. 1. Thereafter,the support and the photosensitive coated layer were cooled to 50° C. orless, and an aqueous solution of 3 wt % polyvinyl alcohol (degree ofsaponification: 86.5 to 89 mol %; degree of polymerization: 1000) wascoated onto the photosensitive coated layer such that the dried coatedweight thereof was 2.0 g/m². Drying was carried out for 90 seconds at100° C. so as to form a sample. The qualities (the ability to withstandrepeated printing, the developability, and the overall quality) wereevaluated for each of the samples. The results are shown in Table 2.

Note that the x, Δ, and ◯ symbols used for the evaluation of quality inTable 2 are defined as follows.

-   -   x . . . did not measure up to quality stipulated by quality        standards (unsatisfactory quality)    -   Δ . . . although no problems in terms of quality standards,        slight faults with respect to quality occurred    -   ◯ . . . no faults with respect to quality

TABLE 2 hot air drying device far infrared radiation heating deviceability to conveying set exit surface set exit surface withstand speedthickness of temperature heating temperature temperature heatingtemperature repeated develop- overall (m/min) support (mm) (° C.) time(sec) (° C.) (° C.) time (sec) (° C.) printings ability quality 10 0.15140 60 135 — — — ◯ X X 0.30 131 ◯ Δ Δ 0.40 119 ◯ ◯ ◯ 15 0.15 45 131 ◯ ΔΔ 0.30 123 ◯ ◯ ◯ 0.40 110 Δ ◯ Δ 20 0.15 30 122 ◯ ◯ ◯ 0.30 108 Δ ◯ Δ 0.4099 X ◯ X 25 0.15 24 109 Δ ◯ Δ 0.30 102 X ◯ X 0.40 93 X ◯ X 0.15 107 3005 122 ◯ ◯ ◯ 0.30 99 109 Δ ◯ Δ 0.40 86 95 X ◯ X 0.15 108 500 132 ◯ Δ Δ0.30 99 118 ◯ ◯ ◯ 0.40 85 108 Δ ◯ Δ 0.15 106 700 152 ◯ X X 0.30 100 141◯ X X 0.40 86 123 ◯ ◯ ◯

As is clear from the evaluations relating to developability in Table 2,when the final temperature reached in either the hot air drying device20 or the far infrared radiation heating device 50 was 130° C. or more,the developability deteriorated. When this temperature exceeded 135° C.,the developing was poor. Further, when the final temperature reached ateither of the hot air drying device 20 or the far infrared radiationheating device 50 was 115° C. or less, the ability to withstand repeatedprintings deteriorated, and when this temperature was 110° C. or less,problems arose with respect to quality.

In a case in which the support and the photosensitive coated layer wereheated by using only the hot air drying device 20 with the heatingcondition being constant (set temperature 140° C.), a sample of anequivalent quality could not be produced if the conveying speed was notadjusted in accordance with the thickness of the support. Conversely, ina case in which an attempt was made to address the problems with respectto quality by making the conveying speed of the support constant andchanging the heating condition by the hot air drying device 20, it wasnecessary to make the conveying speeds of other supports match theconveying speed of the support requiring the largest amount of heat(i.e., the conveying speed of the thickest support), and thus, theproduceability deteriorated.

On the other hand, in a case in which both the hot air drying device 20and the far infrared radiation heating device 50 were used, as comparedwith a case in which only the hot air drying device 20 was used, theconveying speed of the support could be made to be 1.25 to 2.5 timesfaster, and production at a line speed which was equivalent to that forconventional printing plates was possible. Further, by setting theheating conditions of the far infrared radiation heating device 50 inaccordance with a support thickness of 0.15 to 0.40 mm, stableproduction of photopolymer type digital direct printing plates which hadno faults with respect to quality was possible, even with the conveyingspeed of the supports maintained sufficiently fast (25 m/min).

(Specific Example of Manufacturing Schedule of Digital Direct PrintingPlates)

Next, a specific example of a manufacturing schedule of digital directprinting plates in accordance with a conventional method ofmanufacturing lithographic printing plates is shown in Table 3, and aspecific example of a manufacturing schedule of digital direct printingplates in accordance with the method of manufacturing lithographicprinting plates of the present invention is shown in Table 4.

TABLE 3 Conventional Manufacturing Method thickness conveying of supportspeed pattern of changing (mm) (m/min) of width of support heatingconditions 0.15 20 continuous change: hot air drying device large width→ small (constant heating width condition) line stop dummy plate 0.30 15continuous change: large width → small width line stop dummy plate 0.4010 continuous change: large width → small width

TABLE 4 Manufacturing Method in Accordance with the Present Inventionthickness conveying of support speed pattern of changing (mm) (m/min) ofwidth of support heating conditions able to constant: continuous change:{circle around (1)} hot air change 25 m/min large width → small dryingdevice (constant randomly width heating condition) in a range {circlearound (2)} far infrared of 0.15 to radiation heating 0.40 device(automatically changes in accordance with thickness of support and thelike)

As is clear from Tables 3 and 4, with the conventional method ofmanufacturing lithographic printing plates, at the time that digitaldirect printing plates are manufactured, when the thickness of thesupport (aluminum plate) is changed, the production line must betemporarily stopped in order to ensure the quality of the digital directprinting plates. Further, when the support is thick, the conveying speedthereof must be reduced. However, in the method of manufacturing alithographic printing plate of the present invention, even if thethickness of the support changes, there is no need to stop theproduction line, and there is no need to change the conveying speed ofthe support in accordance with the thickness of the support.

As is clear from the above description, in accordance with the methodfor manufacturing a lithographic printing plate of the presentinvention, the conditions for heating a support and a photosensitivecoated layer in a drying and heating process can be change rapidly andin a wide range, and further, the photosensitive coated layer and thesupport can be heated without being contacted.

1. A method for manufacturing a lithographic printing plate, the methodcomprising: conveying a support, on which a photosensitive coatingsolution containing an organic solvent is coated such that aphotosensitive coated layer is formed by the photosensitive coatingsolution; drying the photosensitive coated layer by a first heatingmeans to a dry-to-touch state; heating the support and thephotosensitive coated layer by a second heating means, which does notcontact the support and the photosensitive coated layer, and which isprovided at a downstream side of the first heating means, so thathardening of the photosensitive coated layer is promoted; and changingan amount of heat supplied by the second heating means while the supportis being conveyed, wherein a conveying speed of the support is constantirrespective of a thickness of the support.
 2. The method formanufacturing a lithographic printing plate according to claim 1,wherein a thickness of the support is from 0.15 to 0.40 mm.
 3. Themethod for manufacturing a lithographic printing plate according toclaim 1, wherein a heating condition of the second heating means is setin accordance with the thickness of the support.
 4. The method formanufacturing a lithographic printing plate according to claim 3,wherein the second heating means comprises a far infrared radiationheating device.
 5. The method for manufacturing a lithographic printingplate according to claim 1, wherein the first heating means heats thephotosensitive coated layer to 90° C. or more.
 6. The method formanufacturing a lithographic printing plate according to claim 1,wherein the first heating means dries the photosensitive coated layersuch that a remaining amount of the organic solvent in thephotosensitive coated layer is 5 wt % or less of the photosensitivecoated layer.
 7. The method for manufacturing a lithographic printingplate according to claim 1, wherein a heating system of the secondheating means is a heat radiation system.
 8. The method formanufacturing a lithographic printing plate according to claim 1,wherein a heating system of the second heating means is an inductionheating system.
 9. The method for manufacturing a lithographic printingplate according to claim 1, wherein the condition of heating by thesecond heating means is controlled in accordance with a type of thephotosensitive coated layer formed on the support, such that atemperature of the photosensitive coated layer immediately after heatingby the second heating means is a predetermined temperature which is setin accordance with the type of the photosensitive coated layer.
 10. Themethod for manufacturing a lithographic printing plate according toclaim 1, further comprising forcibly cooling the support and thephotosensitive coated layer by a cooling means provided at a downstreamside of the second heating means.
 11. The method for manufacturing alithographic printing plate according to claim 10, wherein the coolingcomprises blowing air from an air-cooling system toward thephotosensitive coated layer.
 12. The method for manufacturing alithographic printing plate according to claim 10, further comprisingforming an overcoat layer on the photosensitive coated layer after thecooling of the support and the photosensitive coated layer.
 13. Themethod for manufacturing a lithographic printing plate according toclaim 1, wherein a heating condition of the second heating means ischanged within one minute.
 14. A method for manufacturing a lithographicprinting plate, the method comprising: conveying a support, on which aphotosensitive coating solution containing an organic solvent is coatedsuch that a photosensitive coated layer is formed by the photosensitivecoating solution; drying the photosensitive coated layer by a firstheating means to a dry-to-touch state; heating the support and thephotosensitive coated layer by a second heating means, which does notcontact the support and the photosensitive coated layer, and which isprovided at a downstream side of the first heating means, so thathardening of the photosensitive coated layer is promoted; and changingan amount of heat supplied by the second heating means while the supportis being conveyed, wherein a heating condition of the second heatingmeans is changed within one minute.
 15. The method for manufacturing alithographic printing plate according to claim 14, wherein the secondheating means comprises a far infrared radiation heater.
 16. The methodfor manufacturing a lithographic printing plate according to claim 14,further comprising forcibly cooling the support and the photosensitivecoated layer by a cooling means provided at a downstream side of thesecond heating means.
 17. The method for manufacturing a lithographicprinting plate according to claim 16, wherein the cooling comprisesblowing air from an air-cooling system toward the photosensitive coatedlayer.
 18. The method for manufacturing a lithographic printing plateaccording to claim 16, further comprising forming an overcoat layer onthe photosensitive coated layer after the cooling of the support and thephotosensitive coated layer.